Tetraaqua(ethane-1,2-diamine-κ2 N,N′)nickel(II) naphthalene-1,5-disulfonate dihydrate

In the title salt, [Ni(en)(H2O)4]2+·NDS2−·2H2O, the Ni2+ cation is positioned on a twofold rotation axis and exhibits a coordination number of six. The components are connected through an extensive network of O—H⋯O and N—H⋯O hydrogen bonds, and C—H⋯π interactions.

The reaction of ethane-1,2-diamine (en, C 2 H 8 N 2 ), the sodium salt of naphthalene-1,5-disulfonic acid (H 2 NDS, C 10 H 8 O 6 S 2 ), and nickel sulfate in an aqueous solution resulted in the formation of the title salt,
Complexes derived from naphthalene-1,5-disulfonic acid (H 2 NDS) are of great interest in supramolecular chemistry due to their ability to form hydrogen bonds (Shi et al., 2014;Xu et al., 2019;Chen et al., 2020;Suyunov et al., 2023), because the sulfonate group can accept up to six hydrogen bonds with its lone pairs (Oh et al., 2020;Chen et al., 2022).As a ligand, NDS 2À sometimes binds in a bridging mode (Lian & Qu, 2013;Das et al., 2015;Tai et al., 2015).As part of our work in this area, we now describe the synthesis and structure of the hydrated title salt [Ni(en) The asymmetric unit consists of one-half of the [Ni(en)(H 2 O) 4 ] 2+ complex cation, one half of the NDS 2À organic dianion, and a water molecule of crystallization.The Ni 2+ cation in the complex is positioned on a twofold rotation axis and exhibits a slightly tetragonal distortion of the cis-NiO 4 N 2 octahedron.The Ni-N bond length is 2.0782 (16) A ˚, and the Ni-O bond lengths are 2.1170 (13) A ˚and 2.0648 (14) A ˚, similar to those reported for other [Ni(en)(H 2 O) 4 ] 2+ complexes (Healy et al., 1984).The en ligand conformation conforms to the crystallographic twofold axis that passes through it.The NDS 2À dianion exhibits inversion symmetry, with the inversion center located at the middle point of the C5-C5( 3 2 À x, 3 2 À y, 3 2 À z) bond.The structures of the molecular entities are shown in Fig. 1.Neighboring anions have two distinct orientations relative to the complex cation, with the angle between their planes being 55.06 (7) � .The naphthalene ring system exhibits typical bond lengths and angles, with C-C bond lengths ranging from 1.368 (2) to 1.429 (2) A ˚, and C-C-C angles within the range 117.98 (18) to 123.08 (15) � .
In the crystal, the [Ni(en)(H 2 O) 4 ] 2+ cation, the NDS 2À anion, and the water molecules are associated via classical O-H� � �O and N-H� � �O hydrogen bonds (Table 1).Each [Ni(en)(H 2 O) 4 ] 2+ cation forms four N-H� � �O and eight O-H� � �O hydrogen bonds with six neighboring organic anions and two water molecules of crystallization.The four aqua and the en ligands in the cation participate exclusively as hydrogen-bonding donor groups (Fig. 2).All six acceptor O atoms of the SO 3 À groups of the NDS 2À anions participate as double acceptor atoms.It should be noted that the water molecule of crystallization (O3W) is involved in three hydrogen-bonding interactions: two as a donor group with two sulfonate O atoms from two different NDS 2À anions as acceptor atoms, and one as an acceptor group for a hydrogen bond with an aqua ligand.Next to Coulombic interactions, these intermolecular interactions connect the molecular building units into the three-dimensional supramolecular data reports 2 of 3 Suyunov et al. � [Ni(C 2 H 8 N 2 )(H 2 O) 4 ](C 10 H 6 O 6 S 2 )•2H 2 O   IUCrData (2023). 8, x231032   Figure 1 The structures of the molecular entities in the title salt, showing the atomlabeling scheme and displacement ellipsoids drawn at the 50% probability level.H atoms are shown as spheres of arbitrary radius and hydrogen bonds are shown as dashed lines.[Symmetry codes: Table 1 Hydrogen-bond geometry (A ˚, � ).

Figure 2
The structure, as depicted in Fig. 2. As a result of the steric hindrance caused by the sulfonate group, the nearest centroid distance between the naphthalene rings is 6.773 (2) A ˚.There are four notable C-H� � �� interactions between the methylene groups of the en ligands and the naphthalene rings of the NDS 2À anions (Table 1, Fig. 2).

Synthesis and crystallization
The commercially available starting materials were used without further purification.Ethane-

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. Hydrogen atoms attached to nitrogen and those of the water molecules were located in a difference-Fourier map and refined with bond-length restraints of 0.89 (1) and 0.85 (1) A ˚, respectively.

Special details
Geometry.All esds (except the esd in the dihedral angle between two l.s.planes) are estimated using the full covariance matrix.The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry.An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s.planes.

Fractional atomic coordinates
[Ni(C 2 H 8 N 2 )(H 2 O) 4 ]-(C 10 H 6 O 6 S 2 )•2H 2 O or [Ni(en)(H 2 O) 4 ](NDS)•2H 2 O.In the asymmetric unit, one half of an [Ni(en)(H 2 O) 4 ] 2+ cation and one half of an NDS 2À anion, and one water molecule of crystallization are present.The Ni 2+ cation in the complex is positioned on a twofold rotation axis and exhibits a slight tetragonal distortion of the cis-NiO 4 N 2 octahedron, with an Ni-N bond length of 2.0782 (16) A ˚, and Ni-O bond lengths of 2.1170 (13) A ˚and 2.0648 (14) A ˚.The anion is completed by inversion symmetry.In the extended structure, the cations, anions, and noncoordinating water molecules are connected by intermolecular N-H� � �O and O-H� � �O hydrogen bonding, as well as C-H� � �� interactions, forming a threedimensional network.
crystal packing of the title salt in a view along [100].O-H� � �O and N-H� � �O hydrogen bonds are shown as dashed blue lines, and C-H� � �� interactions as dashed green lines.The coordination polyhedron around Ni II is given in the polyhedral representation.

Table 2
Experimental details.
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